1. Field of the Invention
The present invention relates to a luminescence device using an organic electroluminescence (EL) element, a method of driving a luminescence device, and a method of manufacturing a luminescence device.
2. Description of the Related Art
Recently, research and development activities have been flourishing in the field of display devices that have a luminescence element type display panel on which luminescence elements such as organic electroluminescence elements (hereinafter, abbreviated as “organic EL elements”) or the like are disposed in a two-dimensional array, in order to put these devices into full-scale practical and wide use as the next-generation display devices that succeed liquid crystal display (LCD) devices.
An organic EL element includes an anode electrode, a cathode electrode, and, for example, an electron injecting layer, a luminescence layer, a positive hole injecting layer, etc. that are deposited between these electrodes. The organic EL element emits light by energy that is generated when positive holes supplied by the positive hole injecting layer and electrons supplied by the electron injecting layer are recombined in the luminescence layer. As disclosed in Unexamined Japanese Patent Application KOKAI Publication No. 2001-195012, such organic EL elements are used in a display device and driven by Thin Film Transistors (TFTs) or the like that are provided in the respective pixels.
In such a display device, a plurality of pixels each including an organic EL element are generally arranged in the row and column directions and form a matrix. In a case where the TFTs in the pixels are selected row by row through a selecting scan line, the plurality of pixels arranged on the same row are connected through a single current supply line (power feeding line) to a voltage source that causes a current to flow into the respective organic EL elements. Therefore, when the plurality of pixels is to emit light at the same time, a current necessarily flows into the plurality of pixels on the same row at the same time through a single current supply line.
Active matrix display devices that designate a gray level by means of a voltage or a current write a display signal that prescribes the amount of light to be emitted by the organic EL elements into elements that drive the respective pixels by making a current matching the display signal flow into the pixels. Therefore, in a case where the total amount of the currents written into the pixels arranged on the same row is large or in a case where the resistance of the current supply line is not sufficiently low, these display devices would suffer from a problem that the potential of the current supply line easily deviates from the reference value. This causes a problem that the potential varies depending on the length of the current supply line between the voltage source and each pixel, i.e., depending on the position of each pixel and hence the voltage written into the each capacitor varies, making it impossible to obtain a desired luminance. This problem is more remarkable in display devices with a larger area. Particularly, when displaying an image such as a moving image that changes its gray level, these display devices often result in displaying an instable image because such an image requires the total amount of the currents written into the plurality of pixels corresponding to each current supply line to greatly change frame by frame.
Hence, there has been a demand for a luminescence device that can suppress a voltage from decreasing along a current supply line, a method of driving a luminescence device, and a method of manufacturing a luminescence device.
The present invention was made in view of the circumstance described above, and an object of the present invention is to provide a luminescence device that can suppress a voltage from decreasing along a current supply line, a method or driving a luminescence device, and a method of manufacturing a luminescence device.